This invention relates to optical cross-connects for routing multi-wavelength optical signals, and, in particular, to magnetically controllable wavelength-selective optical cross-connects.
In modern telecommunication networks, optical fiber is generally preferred as the transmission medium because of its high speed and wide bandwidth. Wavelength division multiplexing (WDM), which combines many optical signals at different wavelengths for transmission in a single optical fiber, is being used to meet the increasing demands for more speed and bandwidth.
In communication networks, such as those employing WDM, individual optical signals may need to be selectively routed to different destinations. A necessary component for selectively routing signals through interconnected nodes in a communication network is a high capacity matrix or cross-connect switch. At present, most cross-connect switches used in optical communication networks are either manual or electronic. Electronic switches require multiple optical-to-electrical and electrical-to-optical conversions. Because of the speed and bandwidth advantages associated with transmitting information in optical form, all-optical network elements are emerging as the preferred solutions for WDM-based optical networks. Moreover, all-optical network elements are needed to provide the flexibility for managing bandwidth at the optical layer (e.g., on a wavelength by wavelength basis).
Although efforts have been made to develop all-optical cross-connects and switches, these efforts have not kept pace with the ever increasing demands for more speed and bandwidth. For example, some cross-connect arrangements have contemplated a combination of lithium niobate (LiNbO3) switch arrays with fiber amplifiers to address the speed and loss problems of prior systems. Although lithium niobate switch arrays provide fast switching capability and fiber amplifiers can compensate for the lossy characteristics of LiNbO3, these types of cross-connects do not provide the necessary wavelength selectivity for effectively managing bandwidth. In another type of optical cross-connect arrangement, wavelength channels are rearranged according to common destinations using wavelength-changing elements. In particular, multi-wavelength optical signals are demultiplexed into individual optical signals of different wavelengths and the individual optical signals are switched using separate layers of spatial switch fabric corresponding to each of the different wavelengths. The use of demultiplexers and separate layers of switch fabric results in this type of cross-connect arrangement being costly and complex to implement. Similarly, other types of optical cross-connect arrangements using multiple stages of switch fabric are also known to be costly and complex.
In accordance with the invention, an optical cross-connect switch includes an optical router for distributing multi-wavelength optical input signals, an optical combiner for supplying multi-wavelength signals at the output ports of the switch, and optical fibers for interconnecting the optical router and optical combiner. Selected interconnecting optical fibers include controllable wavelength-selective elements, such as magnetically controllable fiber gratings, which are capable of transmitting or reflecting individual channels within the multi-wavelength optical signals so that a selected channel of a particular wavelength can be routed from any of the input ports to any of the output ports of the switch.
In one exemplary embodiment, the optical router portion includes a plurality of input optical couplers, wherein each input optical coupler is associated with a corresponding input port of the optical switch. Similarly, the optical combiner portion includes a plurality of output optical couplers, wherein each output optical coupler is associated with a corresponding output port of the optical switch. Each input optical coupler together with its associated fiber gratings on the interconnecting optical fibers is used for distributing the signals received via the input ports while each output optical coupler together with its associated fiber gratings is used for combining the signals to be supplied at the output ports of the switch. By controlling the transmissive and reflective operating modes of the fiber gratings, the fiber gratings can be used to facilitate the switching of individual channels of the multi-wavelength optical signals on a wavelength by wavelength basis.
The optical cross-connect switch does not require optical-to-electrical and electrical-to-optical conversions and, as a result, can realize the speed and bandwidth advantages associated with transmitting information solely in optical form. Moreover, by using a series of high-speed, magnetically tunable and latchable fiber gratings to facilitate the switching function, the optical switch has the necessary wavelength selectivity to optimally manage bandwidth at the optical layer, e.g., on a wavelength by wavelength basis. The optical switch is also less costly and less complex than the prior arrangements It operates fast and requires no power to maintain the switched state. Additionally, the switch can be assembled and packaged in such a way that the switch performance and the wavelength selectivity are not affected by the changes in ambient temperature.